Turkish President Recep Tayyip Erdogan said Turkey and Russia would discuss the joint production of S-500 defense systems after the S-400 deliveries, local media reported Sunday.

"The S-400 deal is completed. The deliveries are to begin in July or maybe earlier. After that, we will talk about the S-500, including joint production," Erdogan said at an event in Istanbul late Saturday.

"There is absolutely no question of stepping back on the S-400 issue. It is a done deal," the Turkish president was quoted by Anadolu News Agency as saying.

"Sooner or later, we will receive the delivery of the F-35s, and S-400s will come to our country too," he said.

Turkey's S-400 deal has further strained its already tense relations with the United States, which has repeatedly warned Ankara of the risks, including sanctions.

Washington threatens to suspend the delivery of the F-35 fighter jets to Ankara despite its partnership in the consortium, and slap additional sanctions if Turkey continues ahead with the purchase of the S-400s.

In December 2017, Moscow and Ankara signed a loan agreement for the delivery of S-400 systems. NATO and the United States expressed security concerns, saying that S-400s are incompatible with NATO's air defense systems.